1. Field of the Invention
The present invention relates to liquid diphenylmethane diisocyanates (MDI). More specifically, the present invention relates to liquid, alcohol-based, allophanate-modified diphenylmethane diisocyanate prepolymers and the methods of making and using the same.
2. Brief Description of the Prior Art
Liquid diphenylmethane diisocyanates are generally known in the art. U.S. Pat. No. 3,644,457 discloses room-temperature stable liquid isocyanates derived from one mole of diphenylmethane diisocyanate and 0.1 to 0.3 mols of poly-1,2-propylene ether glycol.
U.S. Pat. No. 4,055,548 discloses liquid isocyanate prepolymer compositions obtained by reacting polymethylene polyphenylisocyanate containing from about 65 to 85 percent by weight of methylene bis(phenylisocyanate) with a polyoxyethylene glycol having molecular weight of from 200 to 600 in an equivalent ratio 0.0185-0.15:1.
U.S. Pat. No. 4,115,429 and 4,118,411 disclose low temperature (as low as -5 degrees Centigrade) storage stable liquid diphenylmethane diisocyanates which are produced by reacting diphenylmethane diisocyanates having a specified 2,4-isomer content with propylene glycol or poly-1,2-propylene ether glycol.
U.S. Pat. No. 4,261,852 discloses liquid polyisocyanate compositions comprising (a) the reaction product of 90 to 50% by weight of a reaction product of diphenylmethane diisocyanate and a polyoxypropylene diol or triol having hydroxyl equivalent weight of from 750 to 3000, said reaction product having NCO content of from 8 to 26% by weight, and (B) from about 10 to 50% by weight of a diphenylmethane diisocyanate containing from 30 to 65% by weight of diphenylmethane diisocyanate, the remainder being polymethylene polyphenyl polyisocyanate.
U.S. Pat. No. 4,490,300 discloses room temperature stable liquid isocyanates which are derived by reacting diphenylmethane diisocyanate with an aliphatic diol having a pendant aromatic group, e.g., 2-methyl- 2-phenyl-1,3-propanediol or phenyl-1,2-ethanediol.
U.S. Pat. No. 4,490,300 discloses room temperature stable liquid isocyanates which are derived by reacting diphenylmethane diisocyanate with monoallylether of trimethylolpropane.
U.S. Pat. No. 4,738,991 discloses organic polyisocyanates characterized by allophanate linkages which are prepared by reacting an organic polyisocyanate including 2,4- and 4,4-diphenylmethane diisocyanate with poly or monohydric alcohol in the presence of an organo metallic catalyst. The catalyst is then deactivated using a compound such as an inorganic acid, organic acid, organic chloroformate or an organic acid chloride.
U.S. Pat. No. 4,866,103 discloses a polyisocyanate composition for use in producing elastomers in a RIM process, said composition being the product of reacting an alcohol and or thiol having an average functionality of from about 1.5 to about 4 and an average equivalent weight of at least 500 with at least 2 equivalents per hydroxyl and/or thiol equivalent of an organic polyisocyanate including 4,4- and 2,4-isomers of diphenylmethane diisocyanate under such conditions that at least about 20% of the initially formed urethane and/or thiourethane groups are converted to allophanate and/or thioallophanate groups.
Prior art relating to the preparation of allophanates which contain isocyanates are British Patent 994,890 which relates to the reaction of urethane isocyanates with excess diisocyanate either by heat alone or in the presence of a catalyst such as a metal carboxylate, a metal chelate or a tertiary amine, until the isocyanate content is reduced to that which is obtained theoretically when the complete reaction of the urethane groups is achieved.
U.S. Pat. No. 4,160,080 discloses a process for producing allophanate containing aliphatically and/or cycloaliphatically bound isocyanate groups in which compounds containing urethane groups are reacted with polyisocyanates having aliphatic and/or cycloaliphatic isocyanate groups, in the presence of a strong acid. The process is generally conducted at a temperature of from 90.degree. C. to 140.degree. C. for about 4 to 20 hours.
Japanese Patent Application No. 1971-99176 discloses a method of preparing liquid diphenylmethane diisocyanate by reacting diphenylmethane diisocyanate with aliphatic monovalent alcohol.
By the present invention there is provided a novel liquid isocyanate which is derived from the reaction product of a specified isomer composition of diphenylmethane diisocyanate.